The present invention is directed to a method and circuit arrangement for the redirection of a message cell stream via an alternate route in a cell-oriented communication network.
Such a method and circuit arrangement are already known from Ohta, H. and H. Ueda, "Hitless Line Protection Switching Method for ATM Networks", IEEE International Conference on Communications ICC'93, pages 272 through 276. Given this known method or, respectively, given this known circuit arrangement, a separate control means is respectively provided at the output of a switching equipment located at the start of a line pair as well as at the input of a switching equipment located at the end of the line pair. A message stream to be transmitted is thereby duplicated by the control means located at the appertaining output in order to transmit two identical message cell streams over the line pair to the control means that is located at the end of the line pair and is formed of two line-associated buffers. The latter effects a synchronization of the two supplied message cell streams as well as a forwarding of the message cell stream transmitted over a line of the line pair defined as an alternate route after the synchronization has ensued. Three different methods are described for this. One of these methods amounts to a bit-by-bit comparison of the message cells transmitted over the line pair. In a further method, identical control cells (OAM cells) are inserted into the two message cell streams, whereby the appearance of the control cells is separately monitored in the two buffers. The appearance of a control cell in the leading message cell stream initially forwarded via a selector thereby leads to an interruption of this forwarding. The selector is then redirected with the appearance of a control cell in the trailing message cell stream, so that only this message cell stream if forwarded from this time on. In the remaining method, finally, the control cells are periodically inserted into the two message streams. Only the forwarding of the method cells without switching the selector is thereby triggered by the appearance of the control cells in the trailing message cell stream. Further particulars with respect to the control cells employed and their evaluation in the line-associated buffers, however, cannot be derived from this publication.